Postural invariance in three-dimensional reaching and grasping movements.

Hélène Gréa, Michel Desmurget, Claude Prablanc
Experimental Brain Research. 2000-09-05; 134(2): 155-162
DOI: 10.1007/s002210000427

PubMed

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https://www.bordeaux-neurocampus.fr/12308

1. Exp Brain Res. 2000 Sep;134(2):155-62. doi: 10.1007/s002210000427.

Gréa H(1), Desmurget M, Prablanc C.

Author information:
(1)INSERM U534, Espace et Action, Bron, France.

The question of whether the final arm posture to be reached is determined in
advance during prehension movements remains widely debated. To address this
issue, we designed a psychophysical experiment in which human subjects were
instructed to reach and grasp, with their right arm, a small sphere presented at
various locations. In some trials the sphere remained stationary, while in
others (the perturbed trials) it suddenly jumped, at movement onset, to a new
unpredictable position. Our data indicate that the final configuration of the
upper limb is highly predictable for a given location of the sphere. For
movements directed at stationary objects, the variability of the final arm
posture was very small in relation to the variability allowed by joint
redundancy. For movements directed at « jumping » objects, the initial motor
response was quickly amended, allowing an accurate grasp. The final arm posture
reached at the end of the perturbed trials was neither different from nor more
variable than the final arm posture reached at the end of the corresponding
stationary trials (i.e. the trials sharing the same final object location). This
latter result is not trivial, considering both joint redundancy and the motor
reorganization imposed by the change in sphere location. In contrast to earlier
observations, our data cannot be accounted for by biomechanical or functional
factors. Indeed, the spherical object used in the present study did not
constrain the final arm configuration or the hand trajectory. When considered
together, our data support the idea that the final posture to be reached is
planned in advance and used as a control variable by the central nervous system.